The invention relates to traction chains of the type employed on the tires of heavy duty vehicles, in particular commercial off-road vehicles such as loggers.
It is known to provide heavy duty vehicle traction chains with studs for increased traction on slippery terrain. As shown in U.S. Pat. Nos. 3,768,534 and 4,361,178 (both to Gower), traction studs may be provided on chain links and positioned to protrude radially outwardly from the tire.
Applicant has discovered, however, that although traction studs may be effective on frozen ground, traction protrusions having a larger surface area are more effective on soft ground such as mud and deep snow. As shown in U.S. Pat. No. 4,357,975 to Baldry traction lugs (which are larger in surface area than the studs) may be disposed on centrally located traction rings for providing enhanced traction on soft ground. Applicant has also discovered that lugs are not sufficiently effective on frozen ground due to their inability to significantly penetrate the ground.
Since stud chains are more effective on frozen ground and lug chains are more effective on soft ground, it is presently necessary to have two sets of chains. Not only is this expensive, but in order to optimize traction chain performance, the traction chains must be switched periodically to accommodate various changes in terrain. This a time consuming and labor intensive process since each chain unit for each wheel might weigh from 750 lbs. to over 1500 lbs. Moreover, in certain conditions the ground may be frozen in some places and soft in close by places. This might be the case when there is soft snow near ice, or in the spring when portions of the ground thaw out and become muddy sooner than other portions that remain frozen.
There is a need therefore for a traction chain that is effective on both soft and frozen ground.